Generally, a monopole antenna is comprised of a radiator and a ground plane. In an ideal monopole, the radiator is disposed perpendicular to and separated from an infinite ground plane. With reference to FIGS. 1A-1C, the ideal monopole respectively exhibits a characteristic “half donut” radiation pattern 20, a characteristic two, half-circles elevational radiation pattern 22 relative to an image plane 24 (the image plane being an imaginary plane that is parallel to or coextensive with the ground plane), and a characteristic omnidirectional azimuthal radiation pattern 26 in the image plane 24. Moreover, the electrical field of the electro-magnetic wave that the antenna is capable of producing if the antenna is used to transmit a signal or capable of receiving if the antenna is used to receive a signal is vertically polarized, i.e., the electric field vector is perpendicular to the ground plane.
Generally, a dipole antenna is comprised of a pair of radiators. In an ideal dipole, the radiator structures are coplanar and separated from one another. With reference to FIGS. 2A-2C, the dipole respectively exhibits a characteristic “full donut” radiation pattern 30, characteristic two circle elevational pattern 32 relative to an image plane 34, and a characteristic omnidirectional azimuthal pattern 36 in the image plane. The electrical field of the electro-magnetic wave that the antenna is capable of producing if the antenna is used to transmit a signal or capable of receiving if the antenna is used to receive a signal is vertically polarized, i.e., the electric field vector is perpendicular to the image plane.
Two characteristics of any antenna, including monopole and dipole antennas, are the bandwidth (BW) of the antenna and the voltage standing wave ratio (VSWR) of the antenna. The bandwidth of an antenna is typically defined as the difference between the low frequency (flow) and high frequency (fhigh) at which the power output of the antenna is within 3 dB of the maximum power output of the antenna. The wavelengths associated with flow and fhigh respectively are λlow and λhigh. The VSWR is a measure of how much energy is delivered to the antenna as opposed to how much power is reflected from the antenna. Alternatively, the VSWR is a measure of how closely the antenna impedance and the impedance of the transmitter/receiver associated with the antenna are matched. A VSWR of 1:1 indicates that there is no reflected energy or that the impedances are matched.